General:
* Fantasy: If it refers to a book or film about a royal heir in a fantasy world, then it's likely fantasy.
* Historical Fiction: If it's about a real or fictional heir in a historical setting, then it's likely historical fiction.
* Romance: If it involves a love story with the heir as a central character, then it's likely romance.
* Thriller/Mystery: If it focuses on intrigue, conspiracies, or danger surrounding the heir, then it could be thriller or mystery.
Specific Examples:
* "The Heir Apparent" by Victoria Holt is a historical romance.
* "The Heir Apparent" by Carolyn Jewel is a contemporary romance.
* "The Heir Apparent" by Lisa Kleypas is a historical romance.
* "Heir Apparent" by James Herbert is a horror novel.
To understand the genre of a specific "Heir Apparent" title, you need more context.
Please provide more information about the specific "Heir Apparent" you are interested in, and I can help you determine the genre.